The present application is directed to an interbody device for implantation between a pair of adjacent vertebrae in order to provide support to the vertebrae and/or promote bone fusion between the vertebrae and, in particular, to an interbody device having opposed concave sides with a plurality of laterally opening side channels and a front to rear convex or trapezoidal side view for the upper and lower surfaces.
In the human spine the pad or disc between vertebrae is sometimes damaged or deteriorates due to age, disease, injury, or congenital defect. The vertebrae may also become compressed or otherwise damaged. Vertebrae often become too closely spaced anteriorly due especially to age, but also because of other factors that often produce an undesired abnormal curvature of the spine with respect to lordosis or kyphosis. Because of this, surgery is often utilized to place spacers or interbody devices between the vertebrae which provide proper spacing of the vertebrae and which also promote fusion between the vertebrae. When a device of this type is utilized for the purpose of promoting fusion, it is often referred to as a fusion cage or an intervertebral fusion device. When utilized to promote fusion, bone or bone fusion material is often placed about the interbody devices to promote growth of the bone between the vertebrae. In some procedures, multiple interbody devices are used together and bone fusion material is packed between the pair of devices that are placed in close proximity to one another and extending between the vertebrae to promote growth of bone and, therefore, fusion between the vertebrae.
In the past, interbody devices have typically been either generally rectangular or at least partially cylindrical and threaded. The cylindrical devices have an advantage in that they can be threadably received between and partially into the adjacent vertebrae. For this purpose, the vertebrae are typically first spaced apart, and then a drill is utilized to create a partial bore (radiused channel) in facing surfaces of opposed vertebrae which allows this type of interbody device to be received between the vertebrae. Because of the space between the bones, the interbody device usually engages the bones only along an upper surface and a lower surface of the device. When the interbody device is of a cylindrical threaded type, the upper and lower surfaces are radiused relative to a front to rear axis and such are essentially designed to engage the portion of the vertebrae where bone is removed by boring to create an opening for the device.
When interbody devices are used, it is desirable that such devices engage as much surface of bone as possible to provide support to the bone and to reduce the likelihood of subsidence of the device into the bone, resulting from contact pressure of the interbody spacer against an intervertebral surface of a vertebra. Subsidence can occur since part of the bone is somewhat spongy in nature, especially near the centers of the facing upper and lower surfaces of the vertebrae. The remainder of the structure of the intervertebral device mainly functions to support the two vertebral surfaces, unless the device is also used as a cage within or around which to pack bone fusion material. Because it is also desirable in such structures to maintain weight and volume as low as possible in order to make the device more compatible with the body, it is also desirable to make the entire device as small and lightweight as possible, while maintaining strength. Devices with passthrough windows and other open core structures are limited in strength because of substantial open regions in the core or body of the device.
It is also desirable to minimize the amount of cutting into and reshaping of the vertebral bones to only that which is necessary to correct the structure and function of the spine. Thus, it is desirable to conform an interbody spacer to the shape of the vertebral surfaces of adjacent vertebrae, which surfaces are shallowly concave, rather than conform the vertebrae to the shape of the interbody spacer.
As noted above, age and injury cause the vertebrae to somewhat anteriorly collapse over time. Therefore, it is also desirable for such an interbody spacer to correctly space the vertebrae anteriorly so as to promote normal lordosis or curvature with respect to the spine.
Still further, it is desirable to promote stability of the implant device by promoting bone growth thereabout.